Grinding wheel



Patented May 5, 1942 UNITED STATES PATENT OFFICE I RINDING WHEEL I Samuel S. Kistler, WestBoylston, Mass, assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts No Drawing. Application April 29, 1940,

Serial No. 332,283

2 Claims.

The invention relates to grinding wheels.

One object of the invention is to improve a shellac bonded grinding wheel by the incorporation of an additional substance in the bond. Another object of the invention is to provide an improved bond for the manufacture of Hemming cylinders. Another object of the invention is to reduce the time of gelling of certain specific resins. Another object of the invention is to provide an improved grinding wheel for grinding pocket knife blades, table cutlery and the like. Another object of the invention is to provide a more durable grinding wheel of the shellac bonded variety. Another object of the invention is to provide a grinding wheel bonded at least in part with shellac which is more readily reproducible. Another object of the invention is to reduce rejections in grinding wheels of the char acter indicated? Another object of the invention to provide a grinding wheel of the character indicated which will give a good finish. Another object of the invention is to provide a grinding wheel of the character indicated having a longer life. Another object of the invention is to harden shellac bonded grinding wheels. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, molecular arrangement, and the several steps and relation and order of each of said steps to one or I more of the others thereof, all as will be pointed out hereinafter, andthe scope-of the application of which will be indicated in the following;

For such grinding operations as sharpening pocket knife blades, table cutlery and the like,

Hemming cylinders are used. While the term is I somewhat indefinite, this refers to any grinding wheel of the annular type grinding on the side face which will fit in a Hemming machine or which may be used for grinding cutlery and the like. Hemming cylinders have customarily been v bonded with organic bond, particularly shellac.

The foregoing is illustraceed to make a Hemming cylinder using the following ingredients:

Per cent by weight Crystalline fused alumina, A1203, abrasive 72 Shellac 10.9 Pentaerythritol phthalate, A" stage 4.4 Cryolite 12.7

The foregoing ingredients are placed in a heated kneader or masticator and kneaded for from four to twenty-five minutes. The material is then taken out of the kneader, cooled' and broken up into small lumps. The material is then placed in a mold and hot pressed to the desired size. I have achieved good results pressing the mixture to a specific gravity of 2.73, i. e., a density of 2.73 grams per cubic centimeter. The mold is heated to a temperature of the order of 150 C. and the hot molding is continued for about twenty minutes.

- I then turn cold water onto the outside of the mold until the mold is cool enough to be readily handled. The Hemming cylinder is now stripped from the mold, placed in an oven and baked. A typical and satisfactory baking cycle may be as follows: '48 hours at C. followed by a 24-hour rise to C,, then an 18-hour rise to C., than a 6-hour soak at 160 C.

Shellac appears to be largely an alkyd resin of the intramolecular type in which each m o1e-'- cule in general carries both OH and COOH groups separated by several carbon atoms. The

shellac molecules have relatively high molecular weight, and in view of the large number of carbon atoms per hydroxyl or carboxyl group, .i. e. their wide separation, the rate of further esteriflcation is low and the development of the threedimensional infusible structure is slow. Furthermore, the final product obtained after long heating is not as strong as that of some other alkyds, particularly at elevated temperatures.

9 I have found that it is possible greatly to increase the rate of setting to the infusible mass by the addition of active dicarboxylic or tricarboxylic acids to the shellac. On the other hand, the addition of polyhydric alcohols in general retards the rate of gelling. For example, phthalic anhydride materially reduces the gelling time and maleic anhydride, a stronger acid, reduces the gelling time to a small fraction of its original value. On the other hand, glycerol almost indefinitely extends the gelling time while trimethyl propane or pentaerythritol extend the selling time appreciably.

I believe the explanation of these phenomenon lies in the existence of excess hydroxyl over carboxyl groups in the natural shellac, or a greater ease of reaction with the hydroxyl groups. The active dicarboxylic acids cross-link the large molecules at the hydroxyl groups, while the alcohols tend to reduce the number of carboxyl groups available for cross-linking, a tendency which is partially counteracted by the crosslinking tendencies of the polyhydric primary alcohols.

Therefore, advantage is to be gained by the addition of polycarboxylic acid to a shellac molding compound. I have nevertheless found that a greater advantage is to be gained by the in corporation of both a polybasic acid and a polyhydric primary alcohol, either as such or in the partially reacted form, such as an "A stage alkyd resin.

In order for an alkyd resin madefrom glycerol to be useful for improving heat resistance or gelling time of shellac, it is necessary that the esterification be carried so far that a considerable proportion of the secondary hydroxyl groups are esterified, a very difiicut procedure due to the slow rate of esterification of this group and the aaaama titol, only a dicarboxylic acid, e. g., maleic, succinic, phthalic acid or anhydride thereof, need be I used.

great ease of rehydrolysis. Consequently, the use the sum of the primary hydroxyl groups on the alcohol molecule and the carboxyl groups on the acidmolecule is not less than five, there being at least an equivalent amount of acid in the mix or in the alkyd resin. If the acid ingredient, is Y a dicarboxylic acid there should be at least three primary hydroxyl groups. If the alcohol is dihydric the acid should be at least tricarboxylic. Combinations of polyhydric alcohol and polybasic acid in which the sum of the primary hydroxyl groups on the alcohol molecule and the caiooxyl groups on the acid molecule is not less than five react rapidly and give a strong resin and greatly improve the qualities of shellac, as a cross-linking between the acid and the shellac molecules occurs.

Accordingly, as further examples of the invention, I may substitute for pentaerythritol phthalate in the foregoing example, ethylene glycol and citric acid, either as such or reacted to an "A stage resin. As before stated, the acid should be at least equivalent to the ethylene glycol.

If the alcohol has three or more primary hydroxyls, for example pentraglycerol, trimethylol propane, pentaerythritol, or anhydroenneahep- As further examples of the invention, any of the foregoing may be substituted for the pentaerythritol phthalate in the first example. That is to say, any combination between the acids and the alcohols above given within the foregoing rules may be made.

The proportion of the alkyd resin or combination of alcohol and acid to the shellac may be varied within wide limits. A small amount, for example 5% of the alkyd resin or alcohol and acid, gives good results. Up to of the alkyd resin or combination of alcohol and acid may be used.

1 Grinding wheels made according to the foregoing invention may be more quickly manufactured than shellac wheels. They give an excellent finish to the knives or other articles being ground. The wheels have a longer life than wheels bonded solely with shellac. They also tend to be harder in grinding action.

It will thus be seen that there has been provided by this invention an article in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. An abrasive body comprising abrasive grains united by shellac and from 5% to 75% on the total bond weight of a ,resin which is the reaction product of polyhydric alcohol and polybasic acid, the sum of the primary hydroxyl groups on the alcohol molecule plus the carboxyl groups on the acid from which the resin isderived being not less than five, there having been at least substantially an equivalent amount of acid to react with the alcohol.

2. Method of bonding abrasive grains with shellac comprising adding to the shellac polyhydric alcohol with at least substantially an equivalent amount of acidic substance selected from the groupconsisting of polybasic acids and their anhydrides, selecting such alcohol and acidic substance that the sum of the primary hydroxyl groups on the alcohol molecule plus the carboxyl groups on the acid molecule is at least five, mixing with abrasive grains, placing the mixture in a mold, pressing and heating to react the alcohol and acid with each other and with the shellac.

SAMUEL S. KISTLER. 

